1. Field of the Invention
The invention relates to chemical power supplies, and more particularly to chemical power supplies employing an electrolyte based on an organic solvent.
The invention can be utilized to provide for an independent power supply for electronic devices.
In modern practice, extensive use has been made of chemical power supplies employing an electrolyte based on an organic solvent. However, known chemical power supplies possess poor performance properties. For this reason, the development of novel chemical power supplies possessing better performance properties, is urgent.
2. Prior Art
Known in the art is an electro-chemical current producing cell, comprising a lithium anode, a cathode, a separator adapted for separating the cathode from the anode, and an electrolyte based on an organic solvent (U.S. Pat. No. 3,804,675). The cathode being utilized in said electro-chemical current producing cell is an organic complex consisting of an organic acceptor and an organic donor. The acceptor includes such halogenides as chloranil, bromanil or iodanil. Such compounds as p-phenylene diamine, 3,8-diamino pyrene, dimethyl aniline, tetramethyl-p-phenylene diamine, or 3,10-diamino pyrene may be used as donors. As it is disclosed in the above patent, the preferred combination of the acceptor and the donor is a complex compound comprising chloranil and p-phenylene diamine: ##STR1##
In spite of the fact that the halogenide is soluble in the organic solvents, said complex compound is, as a whole, insoluble in the organic solvents. For this reason said complex compound is mixed in this electro-chemical current producing cell instead of dissolving in the electrolyte based on organic solvents. Such organic solvents as propylene carbonate, gamma-butyrolactone and methyl formate, are utilized. The electrolyte further comprises a light metal salt. Light metal perchlorates, tetrachloroaluminates and tetrafluoroborates can be utilized as said salt.
The separator (diaphragm separating the cathode from the anode) is formed by electrochemical reaction proceeding within said electrochemical current producing cell. ##STR2##
Such a separator consisting of a lithium-chloranil salt, allows the lithium ions to migrate to the cell cathode, and at the same time maintains an electron barrier between the cathode and the anode.
Maximum electromotive force of the above described cell is of 3.25 V.
Said electro-chemical current producing cell is designed for one-time use.
Also known in the art is an electro-chemical current producing cell comprising an anode consisting of an alkali or an alkali-earth metal, a cathode, a separator (diaphragm separating the cathode from the anode) and an electrolyte based on an organic solvent (U.S. Pat. No. 3,578,500).
The most preferred material for the anode, as specified in the above patent, is metallic lithium. As the cathode active material (depolarizer), this cell employs such quaternary salts of organic amines, said salts being soluble in the electrolyte, as for example, N,N,N',N'-tetramethyl diimoniumdiphenoquinone diperchlorate; the tetra cation of N,N,N',N'-tetra-(p-diethylaminophenyl)-p-phenylenediamine; complexes of metals with several common oxidation states; 9,10-phenanthroline ferrous perchlorate; ditrifluoromethyl ethylene dithiolato Ni, Cr, Co; tetracyano ethylene; sulfuryl chloride.
By "active material" is meant an individual substance or a portion thereof, which is directly subjected to electro-chemical redox conversion in the current-forming reaction.
Cathode active materials are dissolved in an organic solvent, said solvent being sulfur dioxide under superatmospheric pressure or dissolved in one of cosolvents. Organic compounds of the elements of groups IIIA, IVA, VA, VIA of the periodic system, comprising one or two unshared pairs of electrons, i.e. ethers, amines, carbonates, etc. are utilized as cosolvents.
The electrolyte based on liquid sulfur dioxide or on sulfur dioxide comprising an organic cosolvent, further comprises a light metal salt, preferably lithium perchlorate and halogenide. Besides, lithium salts of such organic acids as trichloroacetic, formic etc. may be utilized. To prepare an electrolyte in the case of utilization of a cosolvent, a solution of a salt in an organic solvent is saturated with sulfur dioxide under atmospheric or superatmospheric pressure.
The separator element separating the cathode from the anode and obstructing a direct chemical reaction between lithium and a dissolved depolarizer, is a passivating film forming under direct interaction between sulfur dioxide and the anode. This passivating film functions like an ionopenetrable separator. Thus, sulfur dioxide presents the main integral component of such a cell. Along with a chemically formed separator, in the above patent there is also used a Dacron separator to achieve mechanical separation of the cathode from the anode.
Said electro-chemical current producing cell employing a dissolved depolarizer, can operate essentially as a primary power supply, and is much worse when used as a secondary power supply.
Primary power supply means an irreversible cell (battery) designed for one-time use. Secondary power supply means a reversible current producing cell (storage battery) designed for repeated use.
Maximum number of discharge-charge cycles, specified in said patent for such cells, is 8. Electromotive force of the above described electro-chemical current producing cells, depending on the nature of a depolarizer, varies essentially within the range of 2.85 V to 3.85 V, and in two extremal cases is of 3.9 V and 4.0 V. The latter magnitudes are achieved in the case of employing a dication of tetramethyl benzidine. For other systems, the value of electromotive force is much lower.
Employing liquid sulfur dioxide as a solvent in said chemical power supplies imposes some restrictions. First of all, it is a limitation of operating temperature conditions. Since the boiling point of the solvent (sulfur dioxide) is of -10.degree. C., such a cell can operate only at low temperatures, or at higher temperatures under pressure. Moreover, the operating temperature conditions and high toxicity of sulfur dioxide require complex technology, special materials for manufacturing the cell, and certain conditions for its storage and performance. To avoid the explosion of the cell, a special device is to be installed therewithin. The above considerations limit mass application of said cells for domestic purposes.
Furthermore, in numerous chemical reactions sulfur dioxide acts as a reducer, which results in a rather limited choice of cathodes (oxidizers) possessing a high oxidizing potential. Besides, sulfur dioxide reacts with the anode material which fact reduces the service life of the cell.
When using organic cosolvents along with sulfur dioxide, there also arises a need in preliminary passivation of the anode by repeated passing large amounts of sulfur dioxide through the cell. Since in said cell one of the electrodes, i.e. the anode is a solid, the discharge-charge process for such a cell is associated with changing the electrode volume, thereby leading to breakdown of the passivating film which is formed by sulfur dioxide and is a separator. The above fact results in exhaustion of the sulfur dioxide content in the solvent and finally leads to a decrease in capacity, in the number of discharge-charge cycles, and in rapid failure of the current producing cell due to a direct inner reaction between the anode and the depolarizer. Furthermore, since cosolvents employed in the cell are complex organic electron-donor solvents possessing an exclusively low ionization potential, selection of depolarizers having a high oxidizing potential in such solvents to employ said depolarizers as active materials in similar current producing cells, is rather limited.
An important condition of effective operation of said electrochemical current producing cell is also solubility both of oxidized and reduced forms of the depolarizer. However, such most acceptable cathode active materials, specified in the above patent, as organic dications of N,N,N',N'-tetramethyl benzidine, do not meet the above requirements since the products of their reduction are insoluble in the electrolytes being utilized, thereby blocking the cathode and eliminating further electrochemical reaction. This, in turn, leads to a sharp increase in the inner resistance of the cell, thereby significantly lowering the density of the current being collected, excessively increasing charging time, and converting the secondary current producing cell into the primary one, the coefficient of utilization of the cathode active materials being low and a loss of initial capacity being present. Moreover, dications of organic quaternary nitrogen salts in themselves and the more so in nucleophilic media employed in the cell, possess low stability thereby further reducing the number of discharge-charge cycles. Besides, low stability of such organic dications leads to the losses in the capacity of the cell in terms of time, and lowers the shelf life of the cell. The limited range of more or less stable well-known organic dications of quaternary nitrogen derivatives, and of other organic compounds restricts the possibility of selecting these substances as cathode active materials, while the low solubility thereof in the employed electrolytes prevents the development of cells possessing considerable specific capacity. Moreover, high affinity of these dications to nucleophilic reagents restricts the possibility of selecting basic media employed as cosolvents.
A further important limitation in employing such current producing cells is caused by their explosion hazard with moisture getting into the cell, and by the complex technology of manufacturing such cells, which technology requires the presence of constantly inert atmosphere, the absence of moisture, oxygen, and the presence of sulfur dioxide.